I've used MITMproxy for this. It's great fun to MITM every app on your phone, you'll find some really interesting stuff. I happened across a WSDL in the British Airways app that appeared to enable booking flights as if done by a member of staff back of house. It might have been possible to book flights and not pay for them, obviously I didn't go as far to test this. But like I say, interesting stuff.

Tip: Some apps do SSL pinning so the handshake will fail with the cert that your proxy provides. You can disable any kind of SSL cert checks on a jailbroken iOS device with SSL kill switch (https://github.com/iSECPartners/ios-ssl-kill-switch)